1. Field of the Invention
This invention relates to a control device for a vehicular drive system having an electric differential portion, incorporating a differential mechanism for distributing an engine output to a first electric-motor and a power transmitting member, and a transmission portion disposed in a power transmitting path between the electric differential portion and drive wheels. More particularly, it relates to the control device including addressing means to address an issue arising from a case where a drive force is input from output member of the transmission portion in a rotation direction opposite to that in which the output member rotate under a running position.
2. Description of the Related Art
There has heretofore been known a control device for a vehicular drive system which includes an electric differential portion, comprised of a first element connected to an engine, a second element connected to a first electric-motor and a third element connected to a power transmitting member for distributing an engine output to a first electric-motor and a power transmitting member, and a transmission portion i.e., shifting portion disposed in a power transmitting path between the power transmitting member and drive wheels.
For instance, such a control device for the vehicular drive system is disclosed in Patent Publication 1 (Japanese Patent Application Publication No. 2005-264762A1). With the control device for the vehicular drive system, the differential mechanism includes a planetary gear set and the transmission portion includes a step variable automatic transmission portion. An overall drive system establishes an overall speed ratio (total speed ratio) with a speed ratio of the electric differential portion enabled to function as a continuously variable transmission and a speed ratio corresponding to various gear positions (gear shift positions) of the transmission portion. In addition, Patent Publication 1 discloses a shift a shift operation device that can be set to a forward drive running position for performing a forward drive as a running position, in which a power transmitting path between the power transmitting member and the drive wheels is placed in a power transmitting state, and a reverse drive running position for a reverse drive running mode.
Other techniques disclosed in Patent Publication 2 (Japanese Patent Application Publication No. 2005-337372 A1), Patent Publication 3 (Japanese Patent Application Publication No. 2006-44348A1), Patent Publication 4 (Japanese Patent Application Publication No. 2004-150507A1), Patent Publication 5 (Japanese Patent Application Publication No. 2005-176429A1), Patent Publication 6 (Japanese Patent Application Publication No. 2000-8903A1), and Patent Publication 7 (Japanese Patent Application Publication No. 2006-29439A1), Patent Publication 8 (Japanese Patent Application Publication No. 3-32252A1), Patent Publication 9 (Japanese Patent Application Publication No. 9-20161A1), Patent Publication 10 (Japanese Patent Application Publication No. 10-16745A1), Patent Publication 11 (Japanese Patent Application Publication No. 2002-264784A1), and Patent Publication 12 (Japanese Patent Application Publication No. 2001-235015A1) have been known.
With the control device for the vehicular drive system mentioned above, a shift operation device is sometimes set to the running position to allow the power transmitting path between the power transmitting member and drive wheels to be placed in the power transmitting state. When this takes place, a rotation speed of the power transmitting member, i.e., an input rotation speed of the transmission portion, representing an output rotation speed of the electric differential portion, is bound with an output rotation speed relevant value of the vehicular drive system such as rotation speeds of output member of the transmission portion such as, for instance, an output rotation speed of the transmission portion or a vehicle speed, etc.
Here, let's consider about a case wherein, for instance, the shift operation device selects a forward-drive running position under which the vehicle goes back on a slope or the like. In this case, if the drive wheels rotates in a direction opposite to the rotational direction in the forward-drive running position, the power transmitting member is also caused to rotate in an opposite direction. Then, due to the relationship on mutually relative rotation speeds among the rotation speed of the power transmitting member of the electric differential portion, an engine rotation speed and a rotation speed of the first electric-motor, the rotation speed of the first electric-motor increases to a high level. This depends on the engine rotation speed and rotation speed of the power transmitting member, resulting in a likelihood of an adverse affect arising in durability of the first electric-motor.
FIG. 20 is a well-known collinear chart showing the rotation speeds of various rotary elements forming the electric differential portion. In the collinear chart, examples of rotational states of the various rotary elements are plotted for a phase in which a rotational direction of the drive wheels remains in the same direction of the same appearing when a shift position is set to the running position, and another phase in which the rotational direction of the drive wheels becomes opposite to the rotational direction of the same with the shift position set to the running position. In FIG. 20, reference “ENG” represents a rotation speed of a first rotary element (first element) connected to an engine; “M1” a rotation speed of a second rotary element (second element) connected to the first electric-motor; and “M3” a rotation speed of a third rotary element (third element) connected to the power transmitting member.
Respective straight lines represent correlations on the rotation speeds of the various rotary elements. A solid line “a” represents a correlation in which the vehicle goes forward with the shift position being set to a forward-drive running position (“D” position) and the vehicle goes back with the shift position being set to a reverse-drive running position (“R” position). A broken line “b” represents a correlation for the reverse drive (in reverse rotation) of the vehicle under the “D” position and the forward drive (in reverse rotation) of the vehicle under the “R” position.
As shown by the broken line “b”, if the rotational direction of the drive wheels becomes opposite to the rotational direction of the same under the running position, the rotational direction of the power transmitting member takes a negative rotation speed. This causes the rotation speed of the first electric-motor to be liable to increase at a high level in contrast to a phase in which the rotational direction of the drive wheels lies in the same direction under the running position as shown by the solid line “a”.